1. Field of the Invention
The present invention relates to sound reproduction systems and, more particularly, to speaker enclosures for audio reproduction systems. More specifically, the present invention relates to a loudspeaker system having one or more drivers having their back side connected to a duct enclosure that is closed at the bottom end and open at the top end.
2. Description of the Related Art
Transient response test data, (such as waterfall, step, and impulse), taken for practical, commercially-feasible loudspeakers of all types show significant late-arriving acoustic energy. This energy distorts musical notes and transients of all types.
In box speakers most of the residual energy is contained in the air inside of the box. Even with acoustic absorption material in the box, time is required to eventually absorb the energy by friction. Similarly, horn speakers have a cavity behind the dome and/or cone, plus the acoustic resonances (organ pipe) in the length of the horn that accumulate energy.
“Planar” speakers, electro-static or electromagnetic (Magneplanar or “Maggies”) require large frontal areas because of their small displacement capabilities. Part of the surface is further away from the listener, and therefore part of the acoustic wave arrives later than the first part of the wave. Also, planar speakers must stand well away from the wall behind them to minimize reflected wave interference.
A flat panel open back speaker has minimal residual energy (the cone kinetic energy is rapidly damped), but the frontal area has to be impractically large to produce lower bass notes. Also, as with planar speakers, flat panels must stand well away from the wall behind to avoid interference. Bending back the outer portions of a large flat baffle reduces the frontal area while maintaining a sufficiently long acoustic pathway. As the depth increases acoustic resonances (organ pipe) occur and must be addressed.
A need exists to produce a practical loudspeaker having, along with the general capabilities, an excellent bass and transient response as would be provided by obtaining a low residual energy (“LRE”).